Sample preparation

Fluid factors that can enhance the accuracy of the particulate analysis. Such factors include particle dispersion, particle settling, and sample dilution.

Saturation level

The amount of water that can dissolve in a fluid.

Saybolt Universal Viscosity (SUV) or Saybolt Universal Seconds, (SUS)

The time in seconds required for 60 cubic centimetres of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions. (ASTM Designation D 88.)

Scuffing

Abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives.

Scuffing particles

Large twisted and discolored metallic particles resulting from adhesive wear due to complete lubricant film breakdown.

Semisolid

Any substance having the attributes of both a solid and a liquid. Similar to semi liquid but being more closely related to a solid than a liquid. More generally, any substance in which the force required to produce a deformation depends both on the magnitude and on the rate of the deformation.

Shear rate

Rate at which adjacent layers of fluid move with respect to each other, usually expressed as reciprocal seconds.

Shear stress

Frictional force overcome in sliding one "layer" of fluid along another, as in any fluid flow. The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity). The ratio between shear stress and shear rate is constant; this ratio is termed viscosity of a Newtonian fluid, the greater the shear stress as a function of rate of shear. In a non-Newtonian fluid such as a grease or a polymer-containing oil (e.g. multi-grade oil) shear stress is not proportional to the rate of shear. A non-Newtonian fluid may be said to have an apparent viscosity, a viscosity that holds only for the shear rate (and temperature) at which the viscosity is determined.

Silt

Contaminant particles 5 µm and less in size.

Silting

A failure generally associated with a valve which movements are restricted due to small particles that have wedged in between critical clearances (e.g., the spool and bore.)

Single-pass test

Filter performance tests in which contaminant which passes through a test filter is not allowed to recirculate back to the test filter.

Sintered medium

A metallic or non-metallic filter medium processed to cause diffusion bonds at all contacting points.

Sleeve bearing

A journal bearing, usually a full journal bearing.

Sludge

Insoluble material formed as a result either of deterioration reactions in an oil or of contamination of an oil, or both.

Solid

Any substance having a definite shape, which it does not readily relinquish. More generally, any substance in which the force required to produce a deformation depends upon the magnitude of the deformation rather than upon the rate of deformation.

Solvency

Ability of a fluid to dissolve inorganic materials and polymers, which is a function of aromaticity.

Specific gravity (liquid)

The ratio of the weight of a given volume of liquid to the weight of an equal volume of water.

Specific gravity

The ratio of the weight of a given volume of material to the weight of an equal volume of water.

Spectrographic analysis

Determines the concentration of elements represented in the entrained fluid contaminant.

Spectrographic Oil Analysis Program (SOAP)

Procedures for extracting fluid samples from operating systems and analysing them spectrographically for the presence of key elements.

Spin-on filter

A throwaway type bowl and element assembly that mates with a permanently installed head.

Spindle oil

A light-bodied oil used principally for lubricating textile spindles and for light, high-speed machinery.

Splash lubrication

A system of lubrication in which parts of a mechanism dip into and splash the lubricant onto themselves and/or other parts of the mechanism.

Static friction

The force just sufficient to initiate relative motion between two bodies under load. The value of the static friction at the instant relative motion begins is termed breakaway friction.

Stoke (St)

Kinematic measurement of a fluid's resistance to flow defined by the ratio of the fluid's dynamic viscosity to its density.

Strainer

A coarse filter element (pore size over approximately 40 µm)

Suction filter

A pump intake-line filter in which the fluid is below atmospheric pressure.

Sulphated ash

The ash content of fresh, compounded lubricating oil as determined by ASTM Method D 874. Indicates level of metallic additives in the oil.

Sulphurised oil

Oil to which sulphur or sulphur compounds have been added.

Surface fatigue wear

The formation of surface or subsurface cracks and fatigue crack propagation. It results from cyclic loading of a surface.

Surface filtration

Filtration, which primarily retains contaminant on the influent surface.

Surface tension

The contractile surface force of a liquid by which it tends to assume a spherical form and to present the least possible surface. It is expressed in dynes/cm or ergs/cm2.

Surfactant

Surface-active agent that reduces interfacial tension of a liquid. A surfactant used in a petroleum oil may increase the oil's affinity for metals and other materials.

Surge

 momentary rise of pressure in a circuit.

Swarf

The cuttings, and grinding fines that result from metal working operations.

Switch, pressure

An electric switch operated by fluid pressure.

Synthetic lubricant

A lubricant produced by chemical synthesis rather than by extraction or refinement of petroleum to produce a compound with planned and predictable properties.

Synthetic hydrocarbon

Oil molecule with superior oxidation quality tailored primarily out of paraffinic materials.